1. Field of the Invention
The present invention relates generally to a multi-user transmission/reception method and apparatus based on the hybrid beamforming in a millimeter-wave communication system, and more particularly, to a Radio Frequency (RF) precoder configuration method for use in Zero-Forcing (ZF) mode and a limited feedback-based channel information acquisition method of a base station.
2. Description of the Related Art
Millimeter wave transmission is advantageous in transmitting large volumes of data in a high frequency band. Since a millimeter wave has a high frequency and thus makes it possible to narrow the distance between antennas, it is possible for a base station to use more antennas.
In order to compensate for signal attenuation in a millimeter wave channel, it is inevitable for a base station to adopt a beamforming technique. In order to use digital beamforming in a multi-antenna environment, however, there is a limit in view of hardware as well as in the number of RF chains.
In order to address this issue, a hybrid beamforming technique may be used, which consists of digital and analog components. A Radio Frequency (RF) precoder may be configured with an array steering vector such as in legacy analog beamforming, and a baseband precoder may be used for digital beamforming.
FIG. 1 is a diagram illustrating a beamforming technique in a conventional multi-antenna communication system.
Referring to FIG. 1, a sender 110, e.g. base station, includes a baseband precoder 115 and an RF precoder 113 to perform beamforming in hybrid mode. In this case, the sender 110 is provided with a plurality of antennas.
Assuming that the number of transmission and reception antennas is infinite in a single user environment, beamforming can be optimized with Equation (1) using an array steering vector.FRF=[at(φ1t), . . . , at(φtNs)] for |αi|≧|αj|, ∀i<j, FBB:power allocation  (1)
However, the conventional method is limited to single user beamforming, and there is no hybrid beamforming technique suited for the multi-user environment. The conventional method is also susceptible to inter-user interference, which results in performance degradation. The conventional method is based on the assumption of full Channel State Information (CSI) without any detail on the channel feedback mechanism.